Host axons can regenerate through a long nerve allograft if the host is made immunologically tolerant to the transplantation antigens of the graft donor. However, if tolerance is abolished allograft rejection occurs and the host axons in the graft degenerate. Since it was also observed that host axons began a second regenerative effort into the remnants of the rejected nerve a study of the outcome of this regrowth was made. Unfortunately, these axons only grew a short distance into the rejected nerve and then they stopped. This result indicates that an inert connective tissue matrix of nerve will not support the growth of axons over any great distance and that viable Schwann cells are needed. The new immunosuppressive drug Cyclosporin A was found to prevent the rejection of a nerve allograft but when therapy was terminated rejection occurred. This finding means that Cyclosporin A has to be given continually and that short-term treatment does not induce tolerance as others have reported. In another study no evidence was found that freezing a nerve allograft altered its antigenicity. Consequently, no host axons grew through frozen nerve allografts and host animals became sensitized to graft antigens.